kernel: update aes-kw crate and enable zeroize feature

The current version of aes-kw that the SVSM uses does not have a
zeroizing feature that will wipe secrets from memory on drop. Update the
crate to version 0.3.1, which does have this feature.

This brings in a number of API changes, so update the attestation code
making use of the crate accordingly.

Further, aes-kw depends on a newer version of the aes crate than
aes-gcm, or that aes-kw itself did with the previous version. The newer
version of the aes crate renamed the `aes_force_soft` cfg to a generic
`aes_backend="soft"` cfg, so update config.toml as well. Keep the older
`aes_force_soft` cfg, since aes-gcm still depends on the older aes
crate.

Signed-off-by: Carlos López <clopez@suse.de>

Author: 00xc

.cargo/config.toml

@@ -4,6 +4,7 @@
 rustflags = [
 	"-C", "force-frame-pointers",
 	"--cfg", "aes_force_soft",
+	"--cfg", 'aes_backend="soft"',
 	"--cfg", "polyval_force_soft",
 ]
 

Cargo.lock

@@ -69,7 +69,7 @@ virtio-drivers = { git = "https://github.com/coconut-svsm/virtio-drivers.git", r
 
 # crates.io
 aes-gcm = { version = "0.10.3", default-features = false }
-aes-kw = { version = "0.2.1", default-features = false }
+aes-kw = { version = "0.3.1", default-features = false }
 arbitrary = "1.3.0"
 base64 = { version = "0.22.1", default-features = false }
 bindgen = {version = "0.71.0", default-features = false }

Cargo.toml

@@ -21,7 +21,7 @@ elf.workspace = true
 syscall.workspace = true
 
 aes-gcm = { workspace = true, features = ["aes", "alloc", "zeroize"] }
-aes-kw = { workspace = true, optional = true }
+aes-kw = { workspace = true, features = ["zeroize"], optional = true }
 bitfield-struct.workspace = true
 bitflags.workspace = true
 cocoon-tpm-crypto = { workspace = true, features = [

kernel/Cargo.toml

@@ -18,7 +18,7 @@ use crate::{
 #[cfg(feature = "vsock")]
 use crate::{vsock::VMADDR_CID_HOST, vsock::stream::VsockStream};
 use aes_gcm::{AeadInPlace, Aes256Gcm, KeyInit, Nonce, aead::generic_array::GenericArray};
-use aes_kw::{Kek, KekAes256};
+use aes_kw::{KeyInit as _, KwAes256};
 use alloc::{string::ToString, vec::Vec};
 use cocoon_tpm_crypto::{
     CryptoError, EmptyCryptoIoSlices,
@@ -215,20 +215,20 @@ impl AttestationDriver<'_> {
         kdm.extend_from_slice(&(0_u32).to_be_bytes());
         kdm.extend_from_slice(&(256_u32).to_be_bytes());
 
-        let wrapping_key: KekAes256 = {
+        let wrapping_key: KwAes256 = {
             let mut buf = SecretSlice::new_sized(32).or(Err(AttestationError::VecAlloc))?;
 
             concat_kdf::derive_key_into::<sha2::Sha256>(&z, &kdm, &mut buf)
                 .map_err(AttestationError::KeyDerivation)?;
 
-            Kek::new(GenericArray::from_slice(&buf))
-        };
+            KwAes256::new_from_slice(&buf).or(Err(AttestationError::WrapKeyArrayConvert))
+        }?;
 
         let mut cek = SecretSlice::new_sized(&decryption.wrapped_cek.len() - 8)
             .or(Err(AttestationError::VecAlloc))?;
 
         wrapping_key
-            .unwrap(&decryption.wrapped_cek, &mut cek)
+            .unwrap_key(&decryption.wrapped_cek, &mut cek)
             .or(Err(AttestationError::CekUnwrap))?;
 
         let cipher = Aes256Gcm::new(GenericArray::from_slice(&cek));